You could do that but I wouldn't bother. FileVault is full disk encryption and will take a long time regardless of the aggregate amount of data being transferred. It's a background task and doesn't interrupt your work.
Transferring information will take a long time whether you accept the offer to do that during initial setup, or defer it to some other time. Given those two options, doing it during initial setup is simpler and requires less time.
Electing to do it later only conveys the immediate gratification of being able to use a new Mac right away. Lots of people are eager to use their new Mac and understandably choose that option, but then they come back here asking how they can "merge" the two accounts, which can't be done (not easily anyway).
Should you decide to do that though, you already know how: create an initial "dummy" Account that you intend to delete after transferring your "real" Account.